Mechanism of the cis-[Pt(1R,2R-DACH)(H2O)2]2+ intrastrand binding to the double-stranded (pGpG)·(CpC) dinucleotide in aqueous solution: a computational DFT study

Tuning the Reactivity and Bonding Properties of Metal Square-Planar Complexes by the Substitution(s) on the Trans-Coordinated Pyridine Ring

The kinetics of the hydration reaction on trans-[Pt(NH₃)₂(pyrX)Cl]⁺ (pyr = pyridine) complexes (X = OH^-, Cl^-, F^-, Br^-, NO₂ ^-, NH₂, SH^-, CH₃, C≡CH, and DMA) was studied by density functional theory calculations in the gas phase and in water solution described by the implicit polarizable continuum model method. All possible positions ortho, meta, and para of the substituent X in the pyridine ring were considered. The substitution of the pyr ligand by electron-donating X's led to the strengthening of the Pt-N1(pyrX) (Pt-N_pyrX) bond and the weakening of the trans Pt-Cl or Pt-O_w bonds. The electron-withdrawing X's have exactly the opposite effect. The strengths of these bonds can be predicted from the basicity of sigma electrons on the N_pyrX atom determined on the isolated pyrX ligand. As the pyrX ring was oriented perpendicularly with respect to the plane of the complex, the nature of the X···Cl electrostatic interaction was the decisive factor for the transition-state (TS) stabilization which resulted in the highest selectivity of ortho-substituted systems with respect to the reaction rate. Because of a smaller size of X's, the steric effects influenced less importantly the values of activation Gibbs energies ΔG ^⧧ but caused geometry changes such as the elongation of the Pt-N_pyrX bonds. Substitution in the meta position led to the highest ΔG ^⧧ values for most of the X's. The changes of ΔG ^⧧ because of electronic effects were the same in the gas phase and the water solvent. However, as the water solvent dampened electrostatic interactions, 2200 and 150 times differences in the reaction rate were observed between the most and the least reactive mono-substituted complexes in the gas phase and the water solvent, respectively. An additional NO₂ substitution of the pyrNO₂ ligand further decelerated the rate of the hydration reaction, but on the other hand, the poly-NH₂ complexes were no more reactive than the fastest o-NH₂ system. In the gas phase, the poly-X complexes showed the additivity of the substituent effects with respect to the Pt-ligand bond strengths and the ligand charges.

The role of arsenic in the hydrolysis and DNA metalation processes in an arsenous acid-platinum(ii) anticancer complex

Platinum(ii)-based molecules are the most commonly used anticancer drugs in the chemotherapeutic treatment of tumours but possess serious side effects and some cancer types exhibit resistance with respect to these compounds (e.g. cisplatin). For these reasons, the research of new compounds that can bypass this limitation is in continuous development. Recently, mixed Pt(ii)-As(iii) systems have been synthesized and tested as potential anticancer agents. The mechanism of action of these kinds of drugs is unclear. Since in other platinum(ii) containing drugs, hydrolysis plays an important role in the activation of the compound before it reaches DNA, we have explored the aquation process using density functional theory (DFT), focusing our attention on the arsenoplatin complex, [Pt(μ-NHC(CH₃)O)₂ClAs(OH)₂]. As DNA is believed to be the cellular target for Pt anticancer drugs, the metalation mechanism of DNA purine bases has been also investigated. Also for this new drug it appears that guanine is the preferred site with respect to adenine as with other platinum-containing compounds. A comparison with cisplatin is performed in order to highlight the contribution of arsenic in the anticancer activity of this new proposed anticancer agent.

Interactions of the "piano-stool" [ruthenium(II)(η(6) -arene)(quinolone)Cl](+) complexes with water; DFT computational study

Full optimizations of stationary points along the reaction coordinate for the hydration of several quinolone Ru(II) half-sandwich complexes were performed in water environment using the B3PW91/6-31+G(d)/PCM/UAKS method. The role of diffuse functions (especially on oxygen) was found crucial for correct geometries along the reaction coordinate. Single-point (SP) calculations were performed at the B3LYP/6-311++G(2df,2pd)/DPCM/saled-UAKS level. In the first part, two possible reaction mechanisms-associative and dissociative were compared. It was found that the dissociative mechanism of the hydration process is kinetically slightly preferred. Another important conclusion concerns the reaction channels. It was found that substitution of chloride ligand (abbreviated in the text as dechlorination reaction) represents energetically and kinetically the most feasible pathway. In the second part the same hydration reaction was explored for reactivity comparison of the Ru(II)-complexes with several derivatives of nalidixic acid: cinoxacin, ofloxacin, and (thio)nalidixic acid. The hydration process is about four orders of magnitude faster in a basic solution compared to neutral/acidic environment with cinoxacin and nalidixic acid as the most reactive complexes in the former and latter environments, respectively. The explored hydration reaction is in all cases endergonic; nevertheless the endergonicity is substantially lower (by ∼6 kcal/mol) in basic environment. © 2016 Wiley Periodicals, Inc.